SQL-Oracle：解决基本问题的难度，第3部分

Question

So here it is...Produce a list of jobs for departments 10, 50, 20, in that order. Display the job ID and department ID by using the set operators. I have done this so far but i can't do the ordering properly(10,50,20), any ideas?...thanks

SELECT job_id, department_id
FROM (SELECT job_id, department_id
      FROM   employees
      WHERE  department_id IN ('10','20','50')
      INTERSECT
      SELECT job_id, department_id
      FROM   employees
      WHERE  department_id IN ('10','20','50')
      )    
GROUP BY department_id, job_id
ORDER BY COUNT(job_id);

the output is this:

job_ID      department_id

ST_CLERK     50
ST_MAN       50
MK_REP       20
SH_CLERK     50
AD_ASST      10
MK_MAN       20

Answer 1

You can use a CASE statement to implement arbitrary ordering

ORDER BY (CASE department_id
               WHEN 10 THEN 1
               WHEN 50 THEN 2
               WHEN 20 THEN 3
               ELSE 4
           END) ASC

Answer 2

As a note, you could also do instr() :

order by instr(',10,50,20,', ',' || department_id || ',')

The extra commas are to ensure that there are no problems with similar substrings ("110" and "10"). That is not a problem for these particular values, so you could do:

order by instr('10,50,20', department_id)